Many types and mixtures of metal salts and soaps of natural or synthetic organic acids, particularly carboxylic acids, have been suggested and commercially offered over several decades. These have been used to supply metals in forms which are soluble in organic liquids, particularly in various hydrocarbon oils and solvents, to form solutions having various desired properties and uses. For example, such metal salts have found uses as catalysts and as fuel and lubricant additives. Metal salts of carboxylic acids also are useful as stabilizers for various polymers including polyvinyl chloride-type plastics, and in the area of drying catalysts for paints, varnishes and other coating compositions.
The metal salts of carboxylic acids which have been suggested in the prior art include salts formed with a variety of metals including noble and precious metals such as silver, gold, platinum, palladium, osmium, rhodium, iridium, ruthenium, etc. Platinum, its oxides and salts, including organic as well as inorganic salts, have been widely used as catalysts in fuel cells, for abatement of noxious emissions from automobile and industrial exhaust gases, in hydrogenation reactions and in catalytic oxidation reactions such as for preparation of acetic acid, nitric acid from ammonia, etc. Additionally, solutions containing precious metal salts in solvents such as hydrocarbon solvents are particularly desirable. It also is desirable that the solutions of precious metal catalysts be of high purity and essentially free of negative ions which may inhibit certain catalytic reactions.
Stephenson et al, "Carboxylates of Palladium, Platinum and Rhodium, and their adducts," Journal of The Chemical Society (1965) pp. 3632-3640, describes obtaining diacetoplatinum (II) by careful reduction with formic acid of solutions of hexahydroxyplatinate (IV) in acetic acid and preparations of certain rhodium carboxylates are also described. The preparation of diacetoplatinum (II), however, is difficult due to the risk of explosion inherent in the preparation of this compound. This risk has been reported by J. E. Kinsella in CHEM. & IND., pp. 550 (1970) and by E. W. Malerbi, CHEM. & IND., pp. 796 (1970) using a different method. Malerbi also reports that a method to overcome the risk of explosion by Davidson and Triggs reported in the Kinsella, supra, has disadvantages such as that the product is usually contaminated with platinum and the yield tends to be low and variable.
Takiguchi et al, "Synthesis of naphthenates of gold, silver, platinum and palladium and bisoxime palladium dichlorides," Kagyo Kagaku Zasshi, Vol. 72, No.7, (Japan 1969) pp. 1549-1551, describes reactions of chloroauric acid and chloroplatinic acid with sodium naphthenate, reporting that the direct reaction between an aqueous solution of chloroauric acid and sodium naphthenate lacked reproducibility and yield and the direct reactions between chloroplatinic acid and sodium naphthenate caused marked precipitation of metal and "did not produce a good result."
U.S. Pat. No. 3,652,613, issued on Mar. 28, 1972, describes a process for the production of a platinous carboxylate containing two or more carbon atoms by reacting at an elevated temperature a platinic halide with a carboxylate containing two or more carbon atoms of a metal which forms a halide insoluble in the reaction medium. Saturated ethers, carboxylic acids, esters, and ketones are mentioned as suitable inert liquid media. Column 2, lines 1-2, refer to silver carboxylates as "preferred" metal carboxylates.
U.S. Pat. No. 3,700,458 (Lindholm) describes a chemical process for preparing noble metal salts of carboxylic acids useful in photosensitive and thermosensitive compositions. The process involves mixing a non-aqueous solution of an organic carboxylic acid with a non-aqueous solution of a noble metal trifluoroacetate or tetrafluoroborate in the presence of an organic peptizer. A variety of organic peptizers are disclosed including polyvinyl acetals and certain acrylate copolymers.
Vest et al, "Final Technical Report: MOD Silver Metallization for Photovotaics," Department of Energy DOE/JBL/956679--84, Distribution Cat. UC-63 (Purdue Research Foundation, Jul. 1, 1985) pp. 1-52, describes preparation of platinum (II) 2,4-pentanedionate and platinum (II) 2-ethylhexanoate at pages 17 and 18. The preparation of 2,4-pentanedionate is reported as carried out by dissolving potassium tetrachloroplatinate (II) in 8 mL of hot water and stirring in potassium hydroxide dissolved in 2 mL of water. The solution is warmed until it becomes yellow at which time acetyl acetone is added. The report states that when this mixture is heated to 50.degree. C. with frequent shaking, a pale yellow precipitate of platinum 2,4-pentanedionate is gradually formed over a period of 1 to 1.5 hours. The preparation of the 2-ethylhexanoate is reported as prepared by stirring a solution of potassium tetrachloroplatinate into an equal molar mixture of 2-ethylhexanoic acid and triethylamine. The resulting solution is stirred at room temperature for one hour and then heated to 50.degree. C. in a water bath and stirred at that temperature for 2 to 3 hours. The report then states that a black oil separates from this solution which is removed, washed with cold water and then warm water (50.degree.-60.degree. C.) until no chloride ions were detected in the wash water with silver nitrate. The black oil is then extracted in about 40 mL of benzene and dried over a molecular sieve.
Similarly, Vest and Singaram, "Material Research Society Symposium Proceedings", vol. 60, pg. 35 (1986) describes a production of ruthenium 2-ethylhexanoate from ruthenium trichloride trihydrate and triethyl ammonium 2-ethylhexanoate in 68% yield.